This application claims a foreign priority from German patent application 199 39 036.3, filed on Aug. 18, 1999, and the contents of that application are incorporated by reference herein.
This invention involves an arrangement for sweeping of a frequency synthesizer that is digitally tunable in frequency in small steps, through a predetermined progression of frequencies over time with an accumulator that is clocked and generates digital adjustment values for the frequencies.
In frequency synthesizers that are digitally tunable in frequency in small steps, which for example, operate according to a principle of so-called direct digital synthesis (DDS) or of fractional N-divisors, the task often arises of continuously tuning an output frequency in a predetermined progression over time, between a starting frequency and a stopping frequency, i.e. for warbling or sweeping. In a synthesizer with a fractional N-divisor in a reference branch (for example, according to German patent publication Offenlegungsschrift 196 47 474), an output frequency changes, for example, as a function of a reciprocal value of a division factor of a frequency divider controlled by a digital adjustment value, with a sweep speed corresponding to a derivative of the frequency with time; that is it changes as a function of the reciprocal value to the second power. If such a synthesizer is used in a spectrum analyzer, for example, in which measurement values are recorded, or should be to displayed, at equal frequency intervals, this is difficult for such characteristic lines. It is therefore desirable in a synthesizer of this type to maintain a constant sweep speed. Also, in other applications of such synthesizers, it is often desirable to generate a predetermined desired characteristic line progression between frequencies over time, for example, a logarithmic progression.
It is thus an object of this invention to provide an uncomplicated circuit arrangement, which makes it possible to set desired progressions of output frequencies of a synthesizer over time.
According to principles of this invention, an arrangement for sweeping a frequency synthesizer that is digitally tunable in frequency in small steps to have a predetermined frequency progression over time, includes a clocked accumulator for generating digital adjustment values for the frequencies. The arrangement includes a control circuit which is programmed for controlling a clock signal of the accumulator to correspond to a desired frequency progression. Advantageous further embodiments result from inhancements.